JP2598543B2 - Full color copier - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-color copying machine that forms one copied image by repeating a copying process twice for one document image.

[Conventional technology]

In a full-color copying machine, high-level gradation control is the most important technical problem in order to reproduce faithful colors. In general, originals to be copied by a full-color copying machine are mostly those having a center of a halftone portion such as a photograph or a printed matter, and an image formed by full-color copying needs to be uniform without density unevenness. For this reason, in the current analog machine, the gradation at the halftone portion is improved by lowering the potential at the time of development.

In addition, the low-density portion of an image is often formed around a solid portion, and the electrostatic latent image formed by the solid portion on the photoreceptor has an electrolytic strength at a portion corresponding to an edge portion of the solid portion. It is known to grow. Therefore, by reducing the electric resistance of the developer, a substantially uniform amount of toner is adhered to the corners of the solid electrostatic latent image to obtain a copy image without uneven density.

[Problems to be solved by the invention]

However, in the above-described conventional full-color copying machine, although the gradation at the halftone portion can be improved by lowering the potential at the time of development, the saturation density is reduced by this method, so that the gradation at the high density portion is reduced. Will decrease. Further, even when a developer having a small electric resistance is used, if an image has characters or lines drawn on a solid portion, the amount of toner attached to the electrostatic latent image corresponding to the line portion is reduced. The copy image of the copy has lower definition than the solid copy. As described above, in the conventional full-color copying machine, it is difficult to obtain a copy image in a wide gradation range from a low density portion to a high density portion, and the uniformity of the density in the solid portion and the high clarity of characters and lines are obtained. There is a problem that it is difficult to achieve a balance between temperature and temperature.

By the way, as a technique for expanding the dynamic range of a copied image, a superposition method in which different γ characteristics are overlapped, a screen method using a peripheral electric field, and the like have been already put into practical use. Also, a method of inserting a screen filter into the optical path of the reflected light from the document to improve the gradation is well known. It has been confirmed that a method of obtaining one copy image by performing a copy process twice for one image and superimposing the respective color toner images can obtain a copy image having a wide gradation range and a high saturation density. Have been. However, even with the above methods, the fidelity of color reproducibility is in a technically developing stage, and a technology that can reproduce colors with higher fidelity is currently desired. It is.

In view of the foregoing, an object of the present invention is to expand the gradation range and improve the saturation density in a copy image, and particularly to improve the clarity of characters and lines occupying a high density portion.

[Means for solving the problem]

A full-color copying machine according to the present invention is directed to a full-color copying machine that forms a copy image corresponding to a document image by performing a copying process on a document in order to solve the above-described problem. A first copy process for improving the low-density gradation by halftone-decomposing the image information of the original by optical scanning of the original, and a second copy process for applying a higher development potential than the first copy process. That is, one copy image is formed for one document image by executing the above two copy processes.

As the first copying process, for example, a screen filter may be arranged in the optical path of the reflected light from the document.

(Operation)

In the above configuration, by repeating the copying process twice for one original image, a copied image having a wide gradation range from a low density portion to a high density portion and a high saturation density can be obtained. That is, in the first copying process, the reflected light from the document is halftone-decomposed, so that mainly the halftone portion is toned, and the tone region of the low density portion in the copied image can be further expanded. . Then, in the second copying process, a higher developing potential is applied than in the first copying process, so that toner concentrates on the edge portion of the electrostatic latent image during development. The so-called edge effect becomes significant. Therefore, the clarity of characters and lines occupying most of the high-density portion in the copied image can be further improved.

Therefore, even if the original image has characters and lines drawn on the solid portion, a copy image satisfying both the uniformity of density in the solid portion and the high definition of the characters and lines can be obtained.

〔Example〕

One embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

The full-color copying machine according to the present embodiment (hereinafter, simply referred to as a copying machine) has a transparent document table 1 on the upper surface as shown in FIG. An exposure optical system 3 for optically scanning the original 2 and exposing a photoreceptor 4 to be described later is disposed below the original mounting table 1. The exposure optical system 3 includes a light source lamp for irradiating the original 2 placed on the original placing table 1 with light.
3a, a plurality of reflecting mirrors 3b for guiding reflected light from the original 2 onto the photoreceptor 4 as shown by a dashed line in the figure, an imaging lens 3c disposed in the optical path of the reflected light, and a red , Green and blue color filters having three primary color filters.

A belt-shaped photoconductor 4 is provided below the exposure optical system 3. The photoreceptor 4 is driven to rotate over two drive rollers 5 and 6 arranged at a constant interval. Around the drive roller 6 side of the photoconductor 4, a charging charger 7 for charging the photoconductor 4, a cleaning device 8 for removing toner remaining on the photoconductor 4, and an optical path of light reflected from the original 2 are arranged. A screen filter 9 and the like are provided. The screen filter 9 includes, for example, a transparent member such as polyethylene terephthalate and a large number of fine stripes provided on the transparent member. .

On the upper surface side of the photoconductor 4, a developing device 13 having three developing tanks 10 to 12 is arranged in a non-contact state with the photoconductor 4. The developing tanks 10 to 12 have magnet rollers 10a to 12a for adhering toner to the photoreceptor 4, respectively. In addition, yellow, magenta, and cyan color developers, which are complementary colors of the respective color filters in the color separation filter 3d, are individually formed. Is housed. The voltage applied to the charging charger 7 and the developing bias applied to the magnet rollers 10a to 12 are controlled by a control unit 30 described later. On the other hand, below the photoreceptor 4, paper feed cassettes 14 and 15 of different sizes are vertically arranged.
The paper feed rollers 16 and 17 are provided on the paper output side of the paper feeder 15 respectively. Further, a timing roller 18 is provided in the sheet feeding direction of the sheet cassettes 14 and 15.

An intermediate transfer device 19 is provided on the photoconductor 4 on the drive roller 5 side. The intermediate transfer device 19 includes a belt-shaped intermediate transfer body 20, which rotates the intermediate transfer body 20.
It is composed of two drive rollers 21 to 23, transfer chargers 24 and 25, a separation charger 26, a cleaning device 27, and the like. Further, a conveyance belt 28 and a fixing device 29 are provided in the paper exit direction of the intermediate transfer body 20.

 Subsequently, a control system of the copying machine will be described.

As shown in FIG. 1, a control section for controlling each section of the copying machine
The power supply circuit 31 is connected to 30. This power supply circuit 31
Supplies a power to each load in the copying machine, and in particular, a bias circuit 31 for applying a developing bias to the magnet rollers 10a to 12a in the developing device 13 described above.
a, and a high-voltage circuit 31b for applying a high DC voltage to the charging charger 7.

On the other hand, the control unit 30, which also serves as a developing potential control unit, controls the operation of each unit that performs the copying process according to a predetermined program so that one copying image is subjected to two copying processes to form one copying image. Controlling. The control unit 30 controls the photosensitive member 4 charged by the charging charger 7.
Development potential, which is the difference between the surface potential of
The power supply circuit 31 is controlled so that the voltage generated by the bias circuit 31a and the high-voltage circuit 31b in the second copy process is higher than that in the first copy process. To switch.

In the above-described configuration, when performing full-color copying by a copying machine, first, the light source lamp 3a irradiates the original 2 placed on the original placing table 1 with light so that light scanning is performed for three times.
Is done many times. The reflected light from the original 2 enters the color separation filter 3d via the reflection mirrors 3b and the imaging lens 3c, and is separated by the color separation filter 3d for each color component. This light
Further, the light is guided to the screen filter 9 by the reflecting mirrors 3b and 3b, where the halftone dots are decomposed, and then sequentially irradiated on the photoconductor 4 uniformly charged by the charging charger 7, thereby exposing the photoconductor 7. . As a result, an electrostatic latent image for each color component corresponding to the image of the original 2 is formed on the photoconductor 4. At this time, for example, the surface potential of the photoconductor 4 is set to 300V, and the developing bias is set to 100V.

Each of the electrostatic latent images is developed by the developing device 13 with a developer of yellow, magenta, and cyan, which are complementary colors of the color filters in the color separation filter 3d, and is visualized to be a toner image. These toner images for each color component are transferred to the transfer charger 24 in the intermediate transfer device 19.
Are sequentially transferred to the intermediate transfer body 20, and a completed one color toner image is formed by superimposing the toner images for each color component.

Subsequently, the control unit 30 sets the surface potential of the photoconductor 4 to the same as that of the previous copying process, and when the developing bias is set to 80 V and the developing potential becomes high, the above copying process is repeated again. It is. Then, the toner images of the respective color components obtained on the photoreceptor 4 in the second copying process are sequentially transferred onto the color toner image formed on the intermediate transfer member 20 in the first copying process. The two color toner images are superimposed.

The color toner image completed in this way is transferred by the transfer charger 25 to the transfer paper 32 supplied from one of the paper feed cassettes 14 and 15. Thereafter, the transfer paper 32 is separated from the intermediate transfer body 20 by the separation charger 26 and introduced into the fixing device 29 by the transport belt 28, where the transfer paper 32 is subjected to the fixing process of the color toner image. Is done.

In this embodiment, by performing the copying process twice, the gradation range of the copied image can be expanded and the saturation density can be increased. And in the first copy process,
The low-density portion in the copied image is reproduced with the gradation characteristic of the halftone portion further enhanced by the screen filter 9, and in the second copying process, characters and lines occupying most of the high-density portion in the copied image are removed. By increasing the developing potential, the saturation density is increased, and the edge effect becomes remarkable, so that the image is reproduced clearly.

〔The invention's effect〕

As described above, a full-color copying machine according to the present invention provides a full-color copying machine in which a copy process is performed on a document to form a copy image corresponding to the document image. And a second copying process for applying a development potential higher than that of the first copying process. In this configuration, one copy image is formed for one document image by executing one copy process.

According to this, a copy image of a wide gradation range and a high saturation density can be obtained by two copying processes, and a low density portion of the copy image can be obtained by using a screen filter in the first copying process. The tuning range can be further improved. Further, since the development potential is controlled at a higher value in the second copying process than in the first copying process, the edge effect is enhanced so that the clarity of characters and lines occupying most of the high density portion in the copied image is improved. Can be further improved. Therefore, even in the case of an image in which characters and lines are drawn on a solid portion, the density unevenness of the solid portion can be suppressed, and characters and lines can be reproduced with high definition.

[Brief description of the drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a block diagram showing a control system in a full-color copying machine. FIG. 2 is an overall configuration diagram of a full-color copying machine. Reference numeral 3 denotes an exposure optical system, 7 denotes a charging charger, 9 denotes a screen filter, 10a to 12a denote magnet rollers, and 30 denotes a control unit (developing potential control means).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsuyoshi Miyamoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hideyuki Nishimura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Tasuke Uemura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-63-15268 (JP, A)

Claims (1)

(57) [Claims] 1. A full-color copying machine which forms a copy image corresponding to a document image by performing a copy process on the document, wherein the copy process comprises halftone dot decomposition of document image information by optical scanning of the document. And a second copying process for applying a developing potential higher than that of the first copying process. By executing the above two copying processes, 1 A full-color copying machine wherein one copy image is formed for one document image.